The importance of sterile techniques and especially sterile bandage material to modem medicine can hardly be overestimated. Almost every student of biology has heard the tales of how medical practitioners of not too long ago thought that pus and other signs of what is now known to be infection were essential to wound healing. These practitioners would reopen a wound that was not showing the expected pus and inflammation. This was changed by Lister's discoveries regarding disinfection and the subsequent adoption of sterile bandage material for wound dressings. A continuing problem has been the propensity for microorganisms to grow in once sterile bandage material.
A major function of surgical bandages and packing materials is the absorption of various excreted fluids. These fluids are frequently rich in nutrients and are capable of supporting abundant bacterial growth. Since the surgical opening or skin surface is rarely absolutely free of bacteria, the bandage material soon supports a burgeoning bacterial population. These bacteria can easily cause serious infection and may also release a variety of harmful toxins. The obvious solution to such a problem is to change the bandage material often so that bacterial buildup does not occur. An additional approach is to treat the bandage material with some type of disinfectant to limit bacterial growth. Unfortunately, it has proven difficult to produce an effective disinfectant that does not readily wash out of the material. Such wash out, or leaching, reduces effectiveness and may cause irritation or damage to body tissues.
This problem is not limited to bandages, dressings or packings for wounds or surgical incisions. There are a number of instances where absorptive packings are placed in natural body orifices with significant possibility for dangerous bacterial growth. Various nasal packings can become bacterially laden following insertion into nasal passageways. Numerous deaths have resulted from “toxic shock syndrome” resulting from multiplication of Staphylococcus aureus bacteria in feminine care products, particularly tampons. There have been a large number of related problems. For example, U.S. Pat. No. 5,641,503, to Brown-Skrobot, seeks to produce a germicidal tampon and contains a useful list of references to the toxic shock problem. A particular difficulty has been that many potent germicidal agents, e.g. iodine, are partially or totally ineffective in the presence of protein rich solutions such as blood or menses.
In addition, due to the globalization of commerce, the emergence of new diseases, the risks of biological warfare, the contamination of food products with highly pathogenic strains of bacteria, and other forces on society, the uses for a technology that imparts a non-leaching antimicrobial coating to a variety of surfaces is duly recognized. Specific areas of use in addition to bandage material are described below in the Summary of the Invention section.
In connection with the care and treatment of wounds, the term “wound” is meant to include bums, pressure sores, punctures, ulcers and the like. For a long time, one critical aspect of wound care has been the consideration of the requirements of the epithelium, i.e., that area of new cell growth directly peripheral to the wound which is formed during the healing process, so that healing is facilitated.
Since it has been recognized that healing of the wound occurs in one sense as the epithelium migrates by growth from the periphery inward, care has been taken not to damage unnecessarily or to irritate this new area of growth or existing, compromised periwound tissue. With many dressings, problems can occur during dressing changes. This is particularly true where the dressing adheres to the epithelium or where granulation tissue and new cell growth become intertwined within the matrix of a dressing. In these instances, there is a risk that removal of the dressing will damage the sensitive tissue and new growth on the periphery of the wound thereby causing a regression in the progress of wound healing.
Another consideration in wound care is the frequency of dressing changes. The time frame for the changing of dressings depends on many concerns and therefore opinions as to how often dressings should be changed vary drastically.
Still, another important consideration in wound care is the needs of the surrounding unwounded skin. The unwounded skin beyond the epithelium is usually in contact with some portion of the wound dressing system which maintains the dressing positioned on the wound. For example, the surrounding skin may be covered for extended periods with a wrap and/or adhesive to hold the dressing in place. Many such dressings can irritate this surrounding skin and compound problems to the patient. This is especially true in the area of leg ulcers wherein the surrounding skin can easily become sensitized by strong medicaments and is often plagued with flaking, scaling and eczema.
One type of treatment presently used, in particular for leg ulcers, comprises the application of gauze to the ulcer and the utilization of a compression wrap to secure the gauze to the ulcer. Since the gauze quickly becomes saturated, frequent changes are necessary and damage to the epithelium and surrounding skin may occur. Moreover, if the gauze is left on for too long a period, the exudate can begin to overly hydrate and macerate the patient's surrounding skin.
A second type of treatment, also used in particular for leg ulcers, is the Unna's Boot (commercially available from Biersdorf, Inc.) which comprises a zinc paste-containing bandage wrapped around a patient's leg from above the toes to below the knee. Other Unna's Boot/zinc impregnated treatments are available from Miles and Graham Field. These dressings are typically left in place for a week at a time and absorbent pads must be applied to the outside of the dressings in the area of the ulcer to absorb excess exudate. Seepage of exudate throughout the wrap is common, and damage to the skin and epithelium is inevitable.
Another type of wound dressing is disclosed in U.S. Pat. No. 5,106,362 to Gilman. This dressing is provided with a base sheet for contacting the skin of a patient. The base sheet has an opening for placement over the wound. The dressing has a vent for providing controlled leakage of fluid along a path from the wound through the opening of the base sheet. The vent is designed to provide control over wound leakage along a “tortuous path” from the wound through the opening of the base sheet.
A modification of the dressing of U.S. Pat. No. 5,106,362 is disclosed in U.S. Pat. No. 5,056,510, also to Gilman. The '510 patent discloses a vented dressing where the fabric reservoir for wound exudate is contained within a chamber. The walls of the chamber are intended to provide a barrier to bacterial and other contaminants. The walls of the chamber are also intended to be air permeable so as to permit egress of air from the voids of the fabric reservoir. These Gilman dressings do not especially address the problems of the epithelium and the surrounding skin.
It is apparent that, considering the various types of wounds, the numerous dressings that are available, and the various stages of healing, there is still a tremendous need for a dressing that functions better than the current dressings, especially with respect to preventing damage to surrounding skin, tissue and new cell growth. In particular, a wound dressing system which protects the epithelium and surrounding non-wounded skin, which wicks away moisture from the wound area, and which does not purposely adhere to the wound or the surrounding area would be a useful addition to the wound care art. A dressing for patients with fragile skin surrounding a wound would be especially beneficial.
Certain wound dressing materials have been used to absorb exudate and promote healing. For example, Mason, et al., U.S. Pat. No. 4,393,048 teaches a hydrogel composition which, when applied as a powder, absorbs wound exudate. The hydrogel formation may not be complete and lumps of partially hydrated powders form which, when removed, may reopen the wound.
It is known that wounds heal more rapidly and completely if kept in a slightly moist or hydrated state. Polyethylene glycol containing hydrogel wound coverings are disclosed in U.S. Pat. No. 4,226,232, to Spence. These hydrogels cannot be sterilized by irradiation due to the formation of free radicals.
Rawlings et al., U.S. Pat. No. 4,657,006, illustrates wound dressings comprised of a hydrophilic polymer having moisture and vapor permeability properties. However, the exudate absorbed by the hydrophilic polymer tends to harden or solidify the polymer.
An ideal wound dressing should not only absorb exudate but also possess antimicrobial or antibacterial properties. As used in this disclosure, “antibacterial” is defined as having an adverse effect on bacteria, particularly disease-causing bacteria. Furthermore, “antimicrobial” is defined as having an adverse effect on a range of microorganisms, including bacteria and at least some fungi and viruses. An antimicrobial wound dressing is generally preferred over an antibacterial wound dressing.
One example of an antimicrobial wound dressing is Matson, U.S. Pat. No. 4,728,323, which discloses a wound dressing comprising a substrate coated with a coating of a silver salt that allegedly also keeps the wound moist. Since the active agent (silver ion) is not covalently bound to the dressing material, there is a potential for leaching into the body and/or depletion of the active agent.
In the past, wounds have been treated with antimicrobial active agents applied to the wound and covered with a covering that inhibits the healing process. For example, it was conventional practice early in the 20th Century to apply an antiseptic mercury agent such at thimerosal (Merthiolate) or merbromin (Mercurochrome) and the like to a wound and then cover or wrap the wound with a bandage such as gauze or an adhesive strip having a central absorbent gauze portion. A disadvantage of this approach is that the wound often weeps or exudes fluids such as blood, pustulation and the like. While the gauze may absorb some of these fluids, the gauze often adheres to the wound such that removal of the dressing reopens the wound. Advances in the art have been made in both bandages and antimicrobial agents. Certain bandages now contain a nonadhering polymeric coating over or, in place of, the gauze that inhibits the adhering of the absorbent material to the wound but also inhibits the absorption of the exudate that is necessary to properly heal the wound.
Korol, U.S. Pat. No. 4,563,184, discloses wound dressings comprising a polymer, such as poly(2-hydroxyethylmethacrylate), a solvent, such as polyethylene glycol, and a plasticizer such as DMSO. An antimicrobial agent, such as silver sulfadiazine, may be incorporated into the polymeric material.
Widra, U.S. Pat. No. 4,570,629, is drawn to absorbent hydrogel membrane wound dressings made up of hydrophilic biopolymeric copolyelectrolytes comprising a water-soluble linear anionic protein polyelectrolyte component derived from keratin and a water-soluble linear cationic biopolymer polyelectrolyte component derived from either collagen or a glycosaminoglycan. The membranes may also contain antibiotics.
Klemm et al., U.S. Pat. No. 4,191,743, teach the administration of antibiotics to wounds using a wound dressing comprising at least two layers of synthetic resin arranged one above the other having an intermediate layer composed of a synthetic resin granulate having an antibiotic incorporated therein.
Hansen et al., U.S. Pat. No. 5,498,478 is directed to the use of a polyethylene glycol or similar polymer as a binder material for fibers of any variety. The binder and fibers may be pretreated by slurrying the fibers in baths containing antimicrobial agents as part of the solution, thereby causing the fibers and the subsequently formed matrix of polymer and fibers to have an antimicrobial ability.
Mixon et al., U.S. Pat. No. 5,069,907 is directed to the formation and use of a polymeric sheet which may include an antimicrobial agent. This patent teaches of the inclusion of antimicrobial agents into either a pressure-sensitive layer, such as an adhesive, or in a drape used to cover a wound or other sensitive area.
Dietz et al., U.S. Pat. Nos. 5,674,561 and 5,670,557 are directed to polymerized microemulsion pressure sensitive adhesive compositions that may optionally contain antimicrobial and/or other biologically active agents. The potential antimicrobial activity of quaternary amine and quaternary ammonium salts is taught. It is further taught that an antimicrobial agent can be added so as to be contained in a specific layer of a pressure sensitive adhesive device for use as a medical skin covering and/or as a wound dressing.
Young et al., U.S. Pat. No. 5,432,000, teach the use of a polymeric network for adhering particulate materials to a fiber or fibrous product. Specifically, this patent teaches of the use of polymers, such as polyethylene glycol or polyethylene to cause the binding of particulate materials to a fiber, such as cloth. One such particulate member which could be adhered to cloth is an antimicrobial agent, such as epoxide phenol or another antimicrobial substance.
U.S. Pat. No. 5,811,471, to Shanbrom, teaches immobilization of germicidal dyes such as methylene blue onto polyvinyl alcohol gels. The dyes are not covalently bound; however, and thus have the potential to be desorbed. This potential shortcoming is discussed in '471: “Even though dyed PVA appears non-irritating, there might be some concern that the disinfectant dye molecules could migrate to human tissue in contact with the material”. Another potential drawback discussed therein is that the dyes are strongly colored, and hence may not be visually appealing to the consumer: “In the case of some products like tampons a “clean” white product might be psychologically more acceptable”.
In U.S. Pat. No. 4,643,181, Brown discusses mixing an antimicrobial biguanide compound with an adhesive. The adhesive polymer is incorporated into the system to bind the biguanides (which are desorbed from the non-woven material when it is wetted by urine. It is clear from the data that the biguanide antimicrobial leaches from the material, and thus it is a drug-releasing system.
A number of antimicrobial systems based on leaching of low concentrations of silver ion from surfaces have also been reported. For instance, U.S. Pat. Nos. 6,126,931 and 6,030,632 describe a biguanide polymer (PHMB) bonded a substrate. Silver salts are then bonded to the immobilized PHMB. The surface-bound PHMB alone does not inhibit bacterial growth, but it does bind the bacteria, thus allowing the low-solubility silver salts to function.
A similar invention is reported in U.S. Pat. No. 5,662,913, to Capeli, wherein wound dressings which contain silver salts are discussed. The silver is stabilized by polyether polymers.
Another similar method is described in U.S. Pat. No. 5,856,248, to Weinberg, except that copper salts are used instead of silver.
The leaching of silver from elemental silver coatings on medical textiles is described by Tweden et al. (“Silver Modification of Polyethylene Terephthalate Textiles for Antimicrobial Protection”; ASAIO Journal, 43, pM475-M481 (1997). In that study the leaching of silver was equivalent to a serum silver concentration of 55 ppb in an adult human of normal blood volume.
In U.S. Pat. No. 5,985,301, Nakamura describes cellulose fiber that contains silver as an antibacterial agent. In short, cellulose is dissolved in a particular type of solvent, and then silver compounds are added. Fibers are then spun from these solutions. It is reported that these fibers have bactericidal properties. This method must be considered a drug-releasing technology. This fact is emphasized by the following quote from the Nakamura patent: “ . . . enhancing antibacterial effects presumably by promoting the discharge of silver ions from the silver-based antibacterial agent.”
It is known that certain quaternary ammonium salts possess antimicrobial properties. Examples include benzethonium chloride and benzalkonium chloride (BACTINE). It is also known that certain low molecular weight quaternary ammonium groups can be incorporated into polymeric substrates (without chemical bonding) in order to provide certain degrees of antimicrobial activity.
Ionene polymers or polymeric quaternary ammonium compounds (polyquats), i.e., cationic polymers containing quaternary nitrogens in the polymer backbone, belong to a well-known class of biologically-active compounds. See, e.g., A. Rembaum, Biological Activity of Ionene Polymers, Applied Polymer Symposium No. 22, 299-317 (1973). Ionene polymers have a variety of uses in aqueous systems such as microbicides, bactericides, algicides, sanitizers, and disinfectants. U.S. Pat. Nos. 3,778,476, 3,874,870, 3,898,336, 3,931,319, 4,013,507, 4,027,020, 4,089,977, 4,111,679, 4,506,081, 4,581,058, 4,778,813, 4,970,211, 5,051,124, and 5,093,078 give various examples of these polymers, their preparation, and their uses. U.S. Pat. Nos. 3,778,476, 3,898,536, and 4,960,590, in particular, describe insoluble tri-halide containing ionene polymers. U.S. Pat. No. 4,013,507 describes ionene polymers which selectively inhibit the growth of malignant cells in vitro.
Hou et al., U.S. Pat. No. 4,791,063, teach polyionene-transformed modified polymer-polysaccharide separation matrices for use in removing contaminants of microorganism origin from biological liquids. This patent teaches that absorption of bacterial cells by ion-exchange resins is attributable to electrostatic attraction between quaternary ammonium groups on the resin surface and carboxyl groups on the bacteria cell surface.
Chen et al. describe the preparation of antimicrobial dendrimers (highly-branched polymers) having quaternary ammonium functionality (Chen, et al., “Quaternary Ammonium Functionalized Poly(propylene imine) Dendrimers as Effective Antimicrobials: Structure-Activity Studies”, Biomacromolecules 1 p 473-480 (2000)). The compounds described therein are soluble in water; hence, they are not suitable for use as wound dressing materials. The enhanced antimicrobial properties exhibited by polymeric quaternary compounds (relative to monomeric quats), is discussed therein, and also in several other references (Ikeda, T., “Antibacterial Activity of Polycationic Biocides”, Chapter 42, page 743 in: High Performance Biomaterials, M. Szycher, ed., Technomic, Lancaster Pa., (1991); Donaruma, L. G., et al., “Anionic Polymeric Drugs”, John Wiley & Son, New York, (1978); Ikeda T, Yamaguchi H, and Tazuke, S “New Polymeric Biocides Synthesis and Antibacterial Activities of Polycations with Pendant Biguanide Groups”; Antimicrob. Agents Chemother. 26(2), p 139-44 (1984)).
U.S. Pat. No. 6,039,940, to Perrault, teaches a composition and method for treating a wound with an inherently antimicrobial dressing based on quaternary ammonium polymers. The dressing is a hydrogel containing, by weight, about 15 to 95 percent, and preferably about 61 to 90 percent, and most preferably about 65 to 75 percent, cationic quaternary amine acrylate polymer. This polymer is prepared by the polymerization of acryloyloxyethyl(or propyl)-trialkyl(or aryl)-substituted ammonium salts or acrylamidoethyl(or propyl)-trialkyl(or aryl)-substituted ammonium salts. Ultraviolet light is used as the catalyst. The antimicrobial hydrogels are stated to be non-irritating to the wound, absorb wound exudate, and, due to the inherently antimicrobial properties, “enhance the sterile environment around the wound.”
However, the human trial detailed in the '940 disclosure concluded that the measured parameter, the ‘irritation potential’, was “not significantly different from the control”. Analysis of the numerical results indicate that no hydrogel dressing tested gave a better improvement during the test period than the control. This suggests that the use of a hydrogel, although providing a “soothing effect” according to the '940 patent, may not be the optimum dressing for wound healing. Also, it is believed that the present invention offers an advantage over dressing such as the '940 dressing in that the dressing of the present invention are applied a non-gel dressings (e.g., they are dry rather than hydrated). This provides a greater potential for uptake of wound exudates and other aqueous solutions, compared to the '940 hydrogels, which already have water occupying sites in the composition.
Also, the polymers described in the '940 patent are based on acrylate or acrylamide, and as such are susceptible to hydrolysis. Hydrolysis is expected to be greater at high pH or at low pH. It should be noted that these materials are hydrogels, and thus contain a significant amount of water (e.g., 5% to 85%). It also states that the hydrogels are preferably prepared with a physical support structure in order to better retain the hydrogel over a wound. Although the possibility of forming these hydrogels around a web or fibril support is given, it is not clear that the hydrogel material is bonded to the support in any manner. The materials can be dried to powders and later reconstituted. The fact that the hydrogel materials are powders when dry would indicate that shedding of loose hydrogel particles is to be expected. A device wherein the absorbent material is permanently bound to a structural substrate would be more desirable.
The hydrogel materials described by the '940 patent are not breathable. That is, they do not permit unrestricted passage of air through the samples. In that method, the spaces between strands of the “support material” are essentially clogged by hydrated hydrogel material. In the current invention, the individual filaments and fibrils within the substrate are separately “coated” with covalently-bonded antimicrobial polymer. Note that this can be achieved even on a basic raw material such as cotton lint, or wood pulp, which can then be formed into a fabric or other useful structure. Such a process is not possible with the technology described by the '940 patent. In that case, the non-bonded composite must be formed over a prefabricated structure which is a time-consuming process.
The '940 patent also teaches that residual monomer concentrations of up to 3% are acceptable. Such a high level of residual monomer would undoubtedly result in release of active antimicrobial agent into a wound. Monomers such as those used to produce the hydrogels described in the '940 patent are known to cause skin and eye irritation, as well as sensitization (MSDS #14491: Ciba Specialty Chemicals Corporation). While not being bound to a particular theory, another source of leaching of antimicrobial activity may be poor or incomplete cross linking; this may be a source of leaching in that the polymers are only linked to one another, rather to a substrate. It is also difficult and time-consuming to completely wash a hydrogel in order to extract all residual monomer and other leachables without destroying the network structure. The leaching may become greater or less based on ambient conditions of wound exudate. Evidence of leaching from the hydrogel composition are in the '940 patent's summary of the Kirby-Bauer zone of inhibition data. That data, presented in Table 1 of the '940 patent, demonstrate large zones of inhibition, up to 20 mm, around a 5 mm square hydrogel sample. While the '940 patentees meant this data to indicate the antimicrobial effectiveness of the hydrogel, a proper interpretation, in comparison with the non-leaching attributes of the present invention, indicates that the '940 compositions demonstrate a drug-releasing/leaching phenomenon.
In conclusion with regard to the above descriptions of the art, it is apparent that there is a need for an improved dressing that has an effective antimicrobial coating or layer on it, which is covalently bound to a substrate, and is non-leaching upon use.
The antimicrobial activity of a polystyrene fiber containing covalently bonded tertiary amine groups was tested by Endo et al. (“Antimicrobial Activity of Tertiary Amine Covalently Bonded to a Polystyrene Fiber”, Applied Journal of Environmental Microbiology 53(9), p 2050 (1987). Only very slight antimicrobial activity was found for these fibers in the absence of other agents. Significant antimicrobial activity was only observed when these fibers were combined with other antimicrobial agents such as deoxycholate or actinomycin (leachable antibiotics). The material described is based on polystyrene, and thus it is not expected to have physical properties suitable for an absorbent wound dressing material.
The cerium (IV) ion initiated graft polymerization of vinyl monomers onto hydroxyl-containing substrates was first described by Mino (G. Mino and S. Kaizerman; “A New Method for the Preparation of Graft Copolymers. Polymerization Initiated by Ceric Ion Redox Systems”, Journal of Polymer Science 31(22), p 242 (1958)). The mechanism and kinetics of Ce(IV)-initiated graft polymerization of vinylacetate-acrylonitrile onto PVA in water solution was studied by Odian and Kho (G. Odian and J. H. T. Kho; “Ceric Ion Initiated Graft Polymerization onto Poly(vinyl Alcohol)”, J. Macromolecular Science—Chemistry A4(2) p 317-330, (1970)). Later, Vitta et al. described the grafting of methacrylic acid onto solid cellulose substrates (S. B. Vitta, et al., “The Preparation and Properties of Acrylic and Methacrylic Acid Grafted Cellulose Prepared by Ceric Ion Initiation. Part I. Preparation of the Grafted Cellulose”, J. Macromolecular Science—Chemistry A22(5-7) p 579-590 (1985)). None of these references describe antimicrobial materials, or graft polymers based on quaternary ammonium compounds.
A large number of other inventors have labored to produce germicidal bandage and packing materials. U.S. Pat. No. 5,441,742 to Autant et al. discloses a modified cellulosic material with biocidal properties. Unfortunately, water releases the biocidal agents from the material with the concomitant problems of irritation or toxicity towards surrounding tissues. Iodine has been a favored biocidal material. Both U.S. Pat. No. 5,302,392 to Karakelle et al. and U.S. Pat. No. 5,236,703 to Usala rely on polymers containing polyvinylpyrollidone to bind and release iodine. Another approach is shown in U.S. Pat. No. 5,091,102 to Sheridan which relies on the presence of a cationic surfactant to provide germicidal properties to a dry fabric. All of these inventions suffer the problem of having a more or less toxic germicide that can leach from the material.
All patents, patent applications and publications discussed or cited herein are understood to be incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually set forth in its entirety.
From the above review, it is apparent that what is needed in the art of would dressings is a broad spectrum antibacterial or antimicrobial agent that remains in the bandage material where it can prevent bacterial growth, without exerting any negative effects on adjacent living tissue. Similarly, a need also exists for other products to have non-leaching, antibacterial or antimicrobial surfaces to act prophylactically to prevent or reduce the presence of pathogens on such surfaces. Specific examples of such applications of the present technology are provided in the following section.